Devices and methods for performing in-vivo imaging of passages or cavities within a body are known in the art. Such devices may include, inter alia, various endoscopic imaging systems and devices for performing imaging in various internal body cavities
Reference is now made to FIG. 1 which is a schematic diagram illustrating an example of a prior art autonomous in-vivo imaging device. The device 10A typically includes a capsule-like housing 18 having a wall 18A. The device 10A has an optical window 21 and an imaging system for obtaining images from inside a body cavity or lumen, such as the GI tract. The imaging system may include an illumination unit 23. The illumination unit 23 may include one or more light sources 23A. The one or more light sources 23A may be a white light emitting diode (LED), or any other suitable light source, known in the art. The imaging system of the device 10A includes an imager 24, which acquires the images and an optical system 22 which focuses the images onto the imager 24.
In some configurations when a capsule or tube shaped device is used, the imager 24 may be arranged so that its light sensing surface 28 is perpendicular to the longitudinal axis of the device 40. Other arrangements may be used.
The illumination unit 23 illuminates the inner portions of the body lumen through an optical window 21. Device 10A further includes a transmitter 26 and an antenna 27 for transmitting the video signal of the imager 24, and one or more power sources 25. The power source(s) 25 may be any suitable power sources such as but not limited to silver oxide batteries, lithium batteries, or other electrochemical cells having a high energy density, or the like The power source(s) 25 may provide power to the electrical elements of the device 10A.
Typically, in the gastrointestinal application, as the device 10A is transported through the gastrointestinal (GI) tract, the imager, such as but not limited to the multi-pixel imager 24 of the device 10A, acquires images (frames) which are processed and transmitted to an external receiver/recorder (not shown) worn by the patient for recording and storage. The recorded data may then be downloaded from the receiver/recorder to a computer or workstation (not shown) for display and analysis.
During the movement of the device 10A through the GI tract, the imager may acquire frames at a fixed or at a variable frame acquisition rate. For example, in one example the imager (such as, but not limited to the imager 24 of FIG. 1) may acquire images at, for example, a fixed rate of two frames per second (2 Hz) However, other different frame rates may also be used, depending, inter alia, on the type and characteristics of the specific imager or camera or sensor array implementation that is used, and on the available transmission bandwidth of the transmitter 26. The downloaded images may be displayed by the workstation by replaying them at a desired frame rate. In this way, the expert or physician examining the data is provided with a movie-like video playback, which may enable the physician to review the passage of the device through the GI tract.
Decreasing the cross-sectional area of such devices may be limited by the cross-sectional area of the imaging sensor, such as for example the imager 24 of FIG. 1. In order to decrease the size and the cross sectional area of the imaging sensor one may need to reduce the pixel size.
In certain imaging sensors, the area of a single pixel cannot be indefinitely reduced in size because the sensitivity of the pixel depends on the amount of light impinging on the pixel which in turn may depend on the pixel area.
Typically, color imaging in imaging sensors may be achieved by using an array of color pixels. For example, in a color image sensor such as the imaging sensor 24 of the device 10A of FIG. 1, there may be three types of pixels in the imager. Each type of pixel may have a special filter layer deposited thereon. Generally, but not necessarily, the filters may be red filters, green filters and blue filters (also known as RGB filters). The use of a combination of pixels having red, green and blue filters is also known in the art as the RGB color imaging method. Other color imaging methods may utilize different color pixel combinations, such as the cyan-yellow-magenta color pixels (CYMK) method.
The pixels with the color filters may be arranged on the surface of the imager in different patterns. For example, one type of color pixel arrangement pattern is known in the art as the Bayer CFA pattern (originally developed by Kodak™). Other color pixel patterns may also be used.
A problem encountered in the use of RGB color pixel arrays within in-vivo imaging device such as swallowable capsules, or catheter-like devices, or endoscopes, or endoscope like devices, is that for color imaging, one typically needs to use imagers having multiplets of color pixels. Thus, for example in an imager using RGB pixel triplets, each triplet of pixels roughly equals one image pixel because a reading of the intensities of light recorded by the red pixel, the green pixel and the blue pixel are required to generate a single color image pixel. Thus, the image resolution of such a color image may be lower than the image resolution obtainable by a black and white imaging sensor having the same number of pixels. The converse of this is that for a given number of pixels a greater area may be needed for the imager.
A further problem encountered in in-vivo imaging with an autonomous device is the reflection by a turbid media such as liquids or particles floating in a body lumen of light emitted by an illumination unit 23 Such reflected light may cloud or impair an image of a target tissue or wall of a body lumen.
A further problem encountered in in-vivo imaging with an autonomous device is the limitation of images that can be captured to images of the upper surface of a wall of a body lumen. Characteristics such as pathologies of lower layers of tissues may not be clearly visible in in-vivo images captured by prior art autonomous in vivo devices.